Resin clumps cannot be placed in the smithing table.

Steps to recreate:

Open a new world in creative 

Pull the smithing table, any armor trim, any piece of armor, and a resin clump out of the inventory. 

Place down the smithing table

Put the armor and armor trim in the appropriate spot, and try to add the resin clump to the last slot

Resin clumps will not go into the slot